1. Field of the Invention
The invention relates to a hard disk plate, and more particularly, to a texture measuring method of a hard disk plate.
2. Description of the Prior Art
A typical hard disk plate is formed by elecrolessly plating a nickel and phosphorus layer on an aluminum baseboard. The surface of the nickel and phosphorus layer is ground to a roughness (Ra) of 8.about.15 .ANG. followed by mechanical texturing to form circular textures on the surface with a roughness (Ra) of 20.about.40 .ANG.. The final step of the process of forming the hard disk plate involves forming a sputtered base layer, a magnetic layer, a passivation layer and a lubricating layer of approximately 20 .ANG. on the passivation layer.
The hard disk plate comprises a landing zone where a magnetic head may land and a data storage area for storing data. The landing zone has a great number of circular textures to reduce the contact surface between the magnetic head and the hard disk plate. This reduces stiction between them. The data storage area has a smaller number of circular textures so as to provide a better base for positioning the magnetic layer, facilitate operations of the magnetic head, remove oxide on the surface of the nickel and phosphorus layer, and remove scratches generated when grinding the nickel and phosphorus layer.
Removal of scratches is accomplished by mechanical texturing. The thicker the portion of the nickel and phosphorus layer removed, the more scratches will be removed. However, the removal of scratches will result in a rougher data storage area. This will cause problems in the operation of the magnetic head. There are many factors affecting the formation of the circular textures. They include the type of texturing tape, texturing slurry, and coolant, force imposed on the hard disk plate, speed of rotation of the hard disk plate, texturing time, and vibration frequency of the main axis of the hard disk plate. Thus, it is difficult to determine how to form the circular textures.
Currently, the formation of the circular textures is determined based on two numbers. The first number is the difference between the weight of the hard disk plate before and after the circular textures are formed. This value indicates the amount of the hard disk plate removed. The second number is the roughness of the surface of the hard disk plate. This can be directly measured with a measuring device.
The amount of hard disk plate removed is small making accurate measurement of the difference in weight before and after circular texture formation difficult. Moreover, the process is labor intensive as the hard disk plate must be washed and dried before each weighing. Furthermore, the amount of the hard disk plate removed over different areas of the hard disk plate cannot be accurately assessed using the current method. Thus, the flatness of the hard disk plate after forming the circular textures cannot be effectively determined.